George RR Martin, the American author of the fantasy series A Song of Ice and Fire - the source material for the TV drama - announced yesterday that he had missed the December 31 deadline for his eagerly awaited sixth book, The Winds of Winter.

The missed deadline won't affect fans of the TV show, because Martin has already written hundreds of pages and HBO has already filmed the sixth season. Fans of the books are largely sympathetic towards Mr Martin, but are worried there will be plot lines in the TV series, which is to be broadcast in April, that will spoil their enjoyment of the delayed book.

In a post on his website yesterday, 67-year-old Mr Martin told fans that he was "months away" from finishing the sixth instalment. "You wanted an update. Here's the update. You won't like it. The Winds of Winter is not finished. Believe me, it gave me no pleasure to type those words."

It was almost certain, he said, that the book would "not be published before the sixth season of Game of Thrones premieres in April".

He said he had no excuses, but he had a "problem with deadlines" and added he would not set himself another.